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I noticed you seem to have some knowledge about this topic, and I thought I'd
Email to ask you since I just started having this problem myself this morning.
Water overflowed at the place where the rubber hose goes into the pipe connected
To the soil line and there was also some bubbling in the kitchen sink upstairs.
I checked everything else in the house and this seems to be the only problem.
It will be several days before I can take off work to have a plumber in, so I'm
Trying to learn as much as I can about how urgent or complicated this problem
Might be. And, yes, I tried running the spin cycle several times to see if it
Was a fluke, but it keeps happening. And it feels like of like there's an air
Vacuum involved, but I don't understand this vent stuff you're talking about.
I'll have to look and see if I even have one. How can I tell? My house is
About 100 years old and didn't have a washing machine until sometime in the 80s,
Maybe, according to some neighbors. And lots of stuff in the house is strangely
Installed. However, I bought this washer new four years ago when the one that
Came with the house broke just after I moved in. I would think the guy Sears
Sent would have checked things.. . But somehow I think I do not have a vent.
Can you explain this to me? Thanks.

First of all you have a blockage in the washer drain line and it must be snaked and cleared. Let me explain the function of a vent. On a two bath house, as a rule you have three vents. One each on a bathroom lavatory that vents the group, and a kitchen sink vent. If you have a laundry room that could be another vent. Sometimes we tie them all togather in the attic so that we only have one pipe coming out the roof. This is called reventing. A vent that does not terminate through the roof is called a local vent. I am giving these terms so that when you talk to your plumber you will be on the same wave length. A plumbing drainage system has traps on each fixture. These traps keep sewer gas from escaping into your house. On a unvented system the water draining sets up a suction that syphons the water out of the trap letting sewer gas out into your house. I have tried to explain how vents work and the different kinds. You asked how important venting is. Vents are necessary for a plumbing system to function. Get that washer drain snaked. Good luck, Tom

"Thanks so much!!! Is this an "emergency" kind of thing, or can I hold off a week or two on it, provided I don't use the drain to empty the machine during that time?"

This isn't a emergency. However, anything upstream from the washer is going to back up if you drain it. Or, there might be nothing upstream to worry about. Good luck, Tom